The invention relates to the field of steam turbines.
To be more precise, the invention relates to a system intended to be fitted to steam turbines of the type referred to as controlled extraction steam turbines, commonly called controlled bleed steam turbines.
Turbines of the type referred to are encountered in many industrial processes combining generation of electrical power and regulation of the pressure in a steam network. A steam network is fed by bleeding steam from the expansion stage of the turbine. To this end, a bleed control unit controls the extraction pressure, which can be measured, in order to regulate it, either in the vicinity of the control unit or at a relatively distant point in the network.
In the prior art, the bleed control units are of different types to suit the type of turbine and in particular can consist of a control valve or a gate valve.
The control valve is external to the steam flow and operates like a standard control valve. Although in theory it does not have any limitation restricting the extraction pressure, it nevertheless has the drawback of requiring a space for installing it which is of considerable length in the axial direction, generating non-negligible head losses.
The gate valve has a fixed part and a rotary part. It is inserted between two successive stages of the turbine. Referring to FIG. 1, which shows a gate valve, the rotary part (regulator disk) 2a is made up of two concentric rings, namely an inner ring 21a and an outer ring 20a, with the upstream part of the distributor blades 22a between them. The fixed part resembles a diaphragm but carries only the downstream part 12 of the distributor blades, between an outer ring 121 and an inner ring 122. When fully open, the gate valve resembles a standard diaphragm. This configuration is shown in the developed sections of the gate valve distributor blades represented in FIG. 2 (fully open), FIG. 3 (partly open) and FIG. 4 (fully closed). The arrow f shows the direction of the steam.
If P1 is the upstream pressure (see FIG. 1) and P2 the downstream pressure in the steam flow behind the regulator disk 2a, only the downstream (rear) face of the blades 22a is exposed to the downstream pressure P2 and all the rest of the rear face and the front face (upstream face) of the regulator disk 2a are exposed to the upstream pressure P1.
When the disk 2a is fully open, as shown in FIG. 2, the upstream and downstream pressures are the same and it is to this pressure that the downstream face of the blades 22a is exposed, even though it is in contact with the fixed blades 12. However, if the steam flow is slightly obstructed (FIG. 3) head losses are produced and the downstream pressure P2 is lower than the upstream pressure P1, which presses the regulator disk against the fixed part of the gate valve. This is particularly important in the fully closed situation (FIG. 4) in which the downstream pressure P2 is the condenser pressure, for example.
Accordingly, a bleed regulation system of the above kind has the major drawback of being limited to an extraction pressure of approximately 10 to 12 bars. This is because, in the current configuration shown in FIG. 1, the pressure forces acting on the regulator disk 2a are absorbed by the rubbing surfaces between it and the fixed part, rotation inducing unacceptable specific pressures therein if the extraction pressure becomes too high.
An intention of the present invention is to alleviate some of the drawbacks of the prior art.
The invention accordingly provides an integrated bleed regulator system adapted to be fitted to a steam turbine, the system including a fixed part resembling a diaphragm and including a downstream part of distributor blades between an inner ring and an outer ring and a moving part upstream of said fixed part and constituting a regulator disk comprising an upstream part of said distributor blades between an inner ring and an outer ring, in which system said disk, according to its angular position, totally or partially obstructs the steam passage in the upstream to downstream direction or does not obstruct it at all and the surface of said regulator disk downstream of said inner and outer rings is at the upstream pressure, which system is characterized in that means are provided so that at least part of an upstream surface of the assembly formed by the inner and outer rings of the regulator disk communicates with a space downstream of an upstream part of the distributor blades where the pressure is the downstream pressure.
In one embodiment of the invention said means include at least one part forming a counter-abutment with at least a part of the upstream surface of the assembly formed by the inner and outer rings of said regulator disk with a small operating clearance, said regulator disk includes at least one annular groove open on the side facing said counter-abutment part, and at least one passage connects said groove to the space downstream of said upstream part of said distributor blades of the regulator disk where the pressure is the downstream pressure.
According to another feature of the invention said passage opens into a downstream well on the downstream side of said upstream part of the distributor blades of the regulator disk.
Thus, in the invention, it is possible to increase the maximum pressure up to which the steam bleed regulator system can operate correctly.
What is more, the invention involves only a slight increase in overall size compared to a standard gate valve.
In a first embodiment of the invention said counter-abutment part is at the periphery of said fixed part.
In a second embodiment of the invention said counter-abutment part is at the level of the internal bore of said fixed part.
In a third embodiment of the invention said system includes two counter-abutment parts, one of which is at the periphery of said fixed part and the other of which is at the level of the central area thereof.